Analysis And Suppression Of Stray Light In Visible Light Optical System

With the improvement of requirements for observation and tracking capabilities, photoelectric tracking and measuring systems are increasingly using the zoom optical system. Due to the high sensitivity and complex structure, the zoom optical system is susceptible to stray light. So the analysis and suppression of stray light helps to improve the image quality and the observation and tracking capabilities of system. This paper analyzes the influence of rays in the field of view and of small off-axis angle for the stray light on the image plane, and analyzes and designs the light shielding structure for an optical system.First, the basic theory of stray light is studied. The BRDF scattering model and three factors to influence stray light are studied, and the three factors are luminous flux of scattering surface, bidirectional reflectance distribution function BRDF and geometric constituting factor GCF. Through a comprehensive analysis of evaluation methods for stray ligh t, a uniform point source transmittance UPST is defined to evaluate the stray light on image plane. The scope of application for the stray light analysis and principles for the result of stray light suppression are studies. Finally, the suppression methods for stray light are summed up from the optics, mechanics and surface properties.Secondly, through the simulation analysis and experimental testing of an optical-mechanical system, the results prove the reliability of the analysis method. It shows that the stray light of small off-axis angle from 2.20 degree to 2.65 degree forms a clear light spot in the center of the image plane, and by modifying the structure, the light spot is eliminated and the energy of stray light on the image plane reduces a mag nitude. The light spot and its source are got by analysis, and they are the same as the actual testing results. The correctness and accuracy of method and results of software analysis are verified. So this method can be used for subsequent analysis.Thirdly, this paper takes an optical system as the example, analyzing the influence of the normal imaging light in the field of view for the control of stray light on the image plane with that the assembly of variable density disk is placed forward or rearward. The result shows that as the transmittance of variable density disk is 99%, the stray light energy on the image plane when the assembly of variable density disk is placed forward is 10.3% of that when the assembly of variable density disk is placed rearward. So in the optical design, if there are two proper position, the assembly of variable density disk should be placed forward to reduce the stray light.Analysis of the influence for control the stray light on the image plane with the diaphragm for field of view existing or not when the zoom optical system are in telephoto state. The energy of stray light on the image plane with proper diaphragm for field of view is 27% of that without the diaphragm. So the size of diaphragm for field of view in zoom optic al system should be strictly controlled in according to each focal length to suppress stray light.Finally, the design of light shielding structure and the choice of extinction paint for an optical system are conducted. By analysis and calculation, the str ucture and length of the lens hood are reasonably designed and the light barriers with the vertical placement form of easy machining and installation and the tilt top with rounded as selected. And the direction of the tilt angle of the top of the light barrier is designed reasonably according to the needs.